The International Nickel Company of Canada Is Often Cited as an Example

The International Nickel Company of Canada is often cited as an example of monopoly, but International Nickel eventually lost its monopoly.What event was responsible for this?

A) New technology allowed other firms to achieve network externalities after World War II.
B) The Canadian government, which had owned International Nickel, sold the company after World War II. The government no longer blocked entry into the market for nickel.
C) Competition in the market for nickel increased after nickel fields were developed in Russia after World War II.
D) Competition in the market for nickel increased after Canada signed the North American Free Trade Agreement with the United States and Mexico in 1994.